May I ask why these cities? Hanover and Frankfurt are not particularly attractive cities for a tourist, and the jury is still out for Brussels and Luxembourg. Berlin: YES!, but why not combine it with more attractive cities such as Antwerpen, Amsterdam and Munich?

for the BeneluxGermany / Scandinavia / Ireland advice it would help if you give us a bit more info about things you like, where have you been before that you liked, which languages do you speak, etc., etc.